1. Field of the Invention
The invention provides apparatus and method for controlling power flow within a synchronized electric power distribution grid.
2. Background Information
It is an established practice in the generation, transmission and distribution of electric power to interconnect a plurality of polyphase power sources and loads into a "grid" synchronized to have identical frequency, number of electrical phases, and electrical phase angles. Grids may be very large and may include multiple utility systems as well as large numbers of co-generation sites and loads.
In his U.S. Pat. Nos. 5,608,615 and 5,754,420, the inventor teaches apparatus and method for transferring poly-phase electric power from a first grid having a first frequency and first phase to a second grid having a second frequency and second phase without thereby creating harmonic current distortion on either grid, the apparatus comprising a rotating electric machine, having a first winding connected to the first grid, a second winding connected to the second grid and a torque-applying means acting to apply torque between the two windings. The disclosures of U.S. Pat. Nos. 5,608,615 and 5,754,420 are herein incorporated by reference. It is particularly noteworthy that the rotating machine taught in U.S. Pat. Nos. 5,608,615 and 5,754,420 rotated with a speed proportional to the difference in electrical frequency between the two grids.
In his U.S. Pat. No. 5,608,615 the inventor teaches an electric machine structurally similar to a wound rotor induction motor and means of applying a torque thereto, with an angular displacement of the rotor shaft resulting from the application of the torque. U.S. Pat. No. 5,608,615 provides no teaching of the complementary situation of controlling the angular displacement of such a machine and providing means of sustaining the resultant torque.
Within a single power grid there are many interconnections, often in crisscross patterns, that result in multiple paths between two points. Sometimes "loop flow" occurs. For example, 100 Megawatts could be flowing from point A to point B by one route, while 20 Megawatts could be flowing from point B to point A by a different route. A net useable transfer of 80 Megawatts is going from A to B but there are losses associated with the additional 20 Megawatts on both of these routes, and lines on either of the two routes could be overloaded. Consequently, there are occasions when it becomes desirable to force some electric power to flow along a path other than the one with the lowest impedance. That is the subject of this invention.